Microwave power limiter comprising abutting semiconductor and ferrite elements



Feb. 4, 1969 s. DIXON, JR 3,426,299

MICROWAVE POWER LIMITER COMPRESING ABUTTING SEMICONDUCTOR AND FERRITEELEMENTS Filed June 1, 1967 H (OERSTEDS) LENGTH OF MAGNET-.

INVENTOR, SAMUEL DIXON, JR.

A BY M I M c W 1 ATTORNEYS United States Patent 4 Claims ABSTRACT OF THEDISCLOSURE A microwave power limiter which includes respective blocks ofsemiconductor and ferrite materials mounted in a ridged waveguidestructure through which microwave energy is propagated. A magnetic biasis provided to interact with the ferrite material.

Background of the invention This invention relates to a microwavetransmission system utilizing combined gyromagnetic and semiconductorelements and more particularly to the combined gyromagnetic andsemiconductor elements for use in such systems as power limiters.

his well known that gyromagnetic mediums such as ferrites arecharacterized by certain unpaired electron spins which respond to atransmitted microwave signal by precessing gyroscopically about the lineof an applied magnetic field. When the frequency of the applied signalis equal to the natural precession frequency of the electron spins, aresonant condition exists under which the electron spins are able toabsorb large amounts of energy from the signal and thereby greatlyattenuate the signal. Assuming a given resonant D.C. magnetic field, itis characteristic of such ferrites that the signal attenuation is verylow below a critical power P but beyond this point the attenuationincreases linearly due to the resonance effects and, as a result, thepower output remains substantially constant for input power levelsbeyond the critical power level P Power limiting action is therebyachieved. However, with the ferrite biased at subsidiary resonance, theeffectiveness of the ferrite as a power limiter is rather limited atrelatively high power levels.

Summary of the invention It is an object of the present invention toprovide a control for the level of power flow in a microwavetransmission system over a relatively greater dynamic range.

It is a further object of the present invention to provide a powerlimiter for operation at microwave frequencies which provides a flatresponse with very little spike leakage over a relatively large dynamicrange of power level.

In accordance with the present invention there is provided a waveguidemicrowave power limiter which includes a ridged waveguide section havinglongitudinally therein a block of semiconductor material and a block offerrite material, and further including a D.C. magnetic biasing fieldwhich is tapered along the longitudinal dimension of the waveguide.

Brief description of the drawing For a better understanding of theinvention, together with other and further objects thereof, reference ismade to the following description taken in connection with theaccompanying drawing in which:

FIGURE 1 is a perspective view, partially in section, of the presentinvention;

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FIGURE 2 is a sectional view taken along the lines 22 of FIGURE 1; and

FIGURE 3 is an explanatory curve.

Description of the preferred embodiment Referring now to FIGURES 1 and 2of the drawing, at 10 there is shown a ridge waveguide having the narrowor ridge section 12 filled with a block of semiconductor material 14 anda block of ferrite material 16. The semiconductor block 14, preferablycomposed of intrinsic silicon, and the ferrite block 16 aresubstantially of equal dimension so that one half the length of ridgedsection 12 is comprised of the semiconductor bock 14- and the other halfthereof is comprised of the ferrite block 16. As shown, both the blocks14 and 16 are in contact with the top and bottom plates of ridgedwaveguide section 12. Ferrite block 16 may be composed of YIGpolycrystalline material or a suitable nickel-zinc ferrite well known inthe art.

A tapered D.C. magnetic field is arranged along the longitudinaldimension of the ridged section 12 by means of a permanent magnet 18 orany other suitable means well known in the art, to provide a gradientlongitudinally along the semiconductor block 14 and ferrite block 16. Itis to be understood of course that the gradations in the magnitude ofthe biasing field may be supplied by any one of other Well known methodsincluding an electrical solenoid or an electrically energized magnet.Also, the D.C. biasing field is approximately half that required for themain resonance, i.e., the ferrite block 16 is biased substantially tosubsidiary resonance as is well known in the art. The microwave energyextends through and propagates longitudinally through the ridgewaveguide 10 in the conventional manner. A typical variation of theapplied D.C. magnetic field with respect to the longitudinal dimensionof the waveguide 10 is shown in FIGURE 3. The gradient in the magnitudelongitudinally along semiconductor element 14 only affects the ferriteelement 16 and allows the power limiter to operate effectively withrandom variations of the incident power level and frequency. Insofar asthe ferrite block 16 is concerned, at each ferromagnet resonance, thereis a specific critical incidence power beyond which any further increasein incident power produces little or no increase in output power. As theincident power level increases, for example to a level 30 db above thecritical power level P.,, the ferrite block 16 is no longer effectivefor proper limiting action and at approximately this level thesemiconductor block 14 becomes operative to extend the range of thepower limiting action. This is due to the fact that under the influenceof the high power microwave electric field, there is created a solidstate plasma in the semiconductor block 14, due to the phenomenon knownas impact ionization wherein the carriers exhibit the well knownavalanche breakdown characteristic. Thus under the influence of themicrowave electric field, the charge carrier is accelerated until itmakes a collision with the lattice atom of the silicon semiconductorblock 14, and since the mass of the charge carrier is very small incomparison to the lattice atoms, it is reoriented randomly therebyretaining most of the energy gained from the accelerating field. In itsmotion through the crystal lattice, the charge carriers are subjected tovarious loss mechanisms by which its energy is dissipated. If the netloss is below the net gain, avalanche breakdown is achieved. With thephenomenon taking place, the conductivity of the silicon block 14 isgreatly increased so that there is a substantial reduction in impedancein ridge section 12. As a result, the microwave energy now beingpropagated at higher power levels will be reflected back towards theincident microwave source so that power limitation is new extendedbeyond the range for which the ferrite block 16 is normally eifective.

The invention has ben described above with particular reference to asemiconductor of intrinsic silicon. However it will be evident to thoseskilled in the art that the silicon may possess deep lying impuritiessuch as nickel, gold or cobalt.

While the principles of the invention have been described in connectionwith the above specific apparatus, it will be apparent to those skilledin the art that various modifications may be made Without departing fromthe spirit and scope of the invention as set forth in the appendedclaims.

What is claimed is:

1. A device for limiting the power level of microwave energy comprisinga waveguide section, a semiconductor element and a ferrite elementmounted along the longitudinal dimension of said waveguide section, saidelements being in abutment, and means for providing a tapered biasingmagnetic field along said longitudinal dimension.

2. The device in accordance with claim 1 wherein said waveguide sectionis a ridge waveguide.

3. The device in accordance with claim 2 wherein said elements aremounted end to end along said longitudinal dimension.

4. The device in accordance with claim 1 wherein said semiconductorelement is composed of intrinsic silicon and said ferrite element iscomposed of YIG polycrystalline material.

References Cited UNITED STATES PATENTS 2,911,601 11/1959 Gunn et al.333-81 3,131,366 4/1964 Dixon 333-24.2

ELI LIEBERMAN, Primary Examiner.

PQL. GENSLER, Assistant Examiner.

. U.S. Cl. X.R.

